Prosthetic feet are well known in the art. In use, such prosthetic feet typically do not replicate the action of a real foot and may generate “kickback” or “kickforward” reactions that increase the risk of injury to an amputee utilizing the foot. Kickback is motion created by the prosthetic foot in a backward direction during the walking cycle. Kickforward is motion created by the prosthetic foot in a forward direction during the waking cycle. Either motion may create instability for user by expanding or restricting the intended motion. Further, prosthetic feet typically generate vibrations that may travel through a user's leg and cause discomfort.
For an amputee, loosing bipedality may produce an involuntary anterior lean or shift, forcing a constant imbalance or rebalance of posture. The amputee no longer possesses voluntary muscle control on his involved side due to the severance of the primary flexor and extensor muscles. The primary anterior muscle responsible for dorsiflexion (sagittal plane motion) is the anterior tibialis. Dorsiflexion is the voluntary ankle motion that elevates the foot upwards, or towards the midline of the body. The primary posterior muscle responsible for plantarflexion is the gastro-soleus complex, which is a combination of two muscles working in conjunction: the gastrocnemius and the soleus. Plantarflexion is the voluntary ankle motion that depresses the foot downwards, or away from the midline of the body.
There are multiple types of amputations, which require prosthetic limbs. For prosthetic feet there are generally above the knee and below the knee amputations. With below the knee amputations the type of prosthetic foot required often depends on the length of the residual limb of the user. One type of below the knee amputation is known as a Syme's amputation, which is an amputation of the foot through the articulation of the ankle with removal of the malleoli of the tibia and fibula. The Syme's amputation can be one of the best amputations of the lower extremity because it creates a long residual limb and excellent end-bearing stump, which allows for a functionally satisfactory prosthesis. However, due to the length of the residual limb, there is limited space and a compact prosthetic foot is required.